The present invention relates to substantially hydrated cementitious particulates, and more particularly to methods and compositions for introducing admixtures into adhesive, coating, fireproofing, and castable matrix coating compositions.
An xe2x80x9cadmixturexe2x80x9d is a term of art describing materials, other than hydraulic cement, water, and aggregates used for making concrete or mortar, which are added to the batch before or during its mixing.
Admixtures are used for modifying properties of a concrete or mortar. Reasons for using admixtures include: (1) achieving certain physical properties in the resultant cured concrete; (2) improving concrete quality through successive stages of mixing, transporting, placing, and curing during adverse weather or traffic conditions; (3) avoiding particular problems during concreting operations; and (4) reducing construction or labor costs.
Such admixtures, when provided in the form of water-soluble solids or powders, are mixed into the concrete slurry or pre-slurry water at the point of usage. When provided as ready-to-use liquids. Admixtures are typically used in bulk and dispensed directly batch-by-batch into ready-mix trucks at a mix plant.
Successful use of admixtures depends upon the accuracy with which they are prepared and batched. The batching process requires, for each batch of concrete or mortar, careful weighing or volumetric measurement of ingredients before or during introducing them into the mixer. Inaccuracies in measuring the amount of admixture used can significantly affect the performance or physical properties of the concrete or mortar being batched, and consequently may thwart the purpose of including the admixture in the first instance. The need for accurate measurement of the amount of admixture to be added to the batch is particularly acute where relatively small amounts are required.
Attempts have been made to overcome the difficulties involved in handling, measuring, and dispensing free-flowing fluid, semi-fluid, and solid admixtures. In U.S. Pat. No. 4,961,790 Smith et al. disclosed water-soluble containers that released solid or powdered admixtures when the container was dissolved within a wet mixer. On the other hand, Valle et al. disclosed in U.S. Pat. No. 5,203,629 a non-water-soluble packaging that disintegrated under the grinding effect of the wet concrete mix, thereby releasing admixtures throughout the concrete. In U.S. Pat. No. 5,320,851 DeMars et al. disclosed a disintegratable gelatin or wax capsule for introducing fluid or semi-fluid admixtures into the concrete mix.
Attempts have also been made to dispense certain admixtures in powdered or compacted dry form. U.S. Pat. No. 4,284,433 of Aignesberger et al. disclosed solid pelletized additives composed of a naphthalenesulphonic acid derivative-formaldehyde condensate, a resin based on an amino-s-triazine with at least two NH2 groups and modified with sulphite or sulphonic acid, a sulphite- or sulfonic acid-modified melamine-formaldehyde poly-condensate, a copolymer based on styrene and acrylonitrile, a lignin sulfonate, or a phenol-sulphonic acid-formaldehyde polycondensation product.
A similar concept was disclosed in U.S. Pat. No. 5,728,209 of Bury et al. wherein a certain amount of powder or flake cement admixture material was pressed into a compacted unit that was designed to dissolve or break apart in a cementitious mixture such as wet concrete. The compacted unit was intended to have strength sufficient to maintain structural integrity during handling and storage, while having solubility or friability upon agitation in a wet concrete mix.
In U.S. Pat. No. 5,236,501, Nomachi et al. disclosed a method for coating cement particles involving aerial rotation of dry powdered cementitious particles and spraying the swirled particles with water, which optionally contained an admixture such as a water reducing agent.
Another coating method was disclosed in U.S. Pat. No. 5,766,323 of Butler et al. Hydrophobing additives were coated onto carrier particles, such as starch, methyl cellulose, carboxymethyl cellulose, cement, sand, silica, fly ash, alumino silicates, clay materials, lime, calcium carbonates, polystyrene beads, and polyacrylate beads. For example, Butler et al. described spraying an organopolysiloxane material and a binder material (e.g., polyvinyl alcohol) onto the outer surface of carrier particles using a fluidized bed to solidify the organopolyxiloxane and binder, through cooling or evaporation of solvent, onto the carrier particle surface.
The present inventors, however, believe that methods involving dry-compacting of admixtures and coating of carrier particles with admixtures are complicated and laborious. Typically, admixtures for concrete and mortar are supplied in liquid form, because they are manufactured as liquids. Considerable costs and time would be spent to dry them, to compact them, to pelletize or granulate them by fluidized bed coating evaporative methods. Even simpler forms of coating, such as using carrier particle materials such as vermiculite and zeolites, which have high surface areas, would be expensive and may introduce unwanted materials into a concrete, mortar, or grout composition.
In view of the disadvantages of the prior art, what are needed are a novel process for manufacturing a solid admixture system, a novel admixture, and a novel method for modifying hydratable cementitious compositions such as concrete, mortar, masonry, grout, and other matrix compositions.
In contrast to prior art methods, particularly those methods in which admixture(s) are coated onto carrier particles, the present inventors have devised a novel process whereby at least one admixture is introduced into matrix and coating compositions such as castable cementitious compositions (e.g., concrete, mortar, fireproofing, shotcrete) and coatings (e.g., paints, primers) and other compositions (e.g., adhesives, mastics).
More significantly, the present invention pertains to high-surface area containing particulates which are formed from at least one substantially hydrated cementitious binder and comminuted to an average particle diameter of 5 to 250 micrometers (and up to 6 centimeters or more). Admixtures can be intermixed with the cementitious binder before it is hardened and comminuted into the particulates. Alternatively, or in addition to having admixture(s) and/or additives intermixed into the particulates, the admixtures and/or additives may be coated onto the surface of the comminuted particulates at relatively high addition rates. Thus, an exemplary process of the invention comprises: intermixing a hydratable cementitious binder and water to obtain a hydratable cementitious slurry; allowing said slurry to harden into a substantially hydrated mass; and comminuting the hardened mass into a plurality of particulates having an average particle diameter of 5 to 250 micrometers. The particulates can be as high as 6 centimeters for purposes of delivering cement additives in clinker intergrinding processes. Exemplary hydratable cementitious binders include Portland cement, gypsum, plaster, optionally with one or more pozzolans. The binder is mixed with water to form a paste (or slurry) that is then allowed to hydrate substantially into a solidified mass which is comminuted into particulates.
In a preferred method of the invention, at least one admixture is intermixed with the binder before it is hardened into a mass and comminuted into particulates. Mix water may be added directly to the one or more admixture(s), binder, or both at once, or incorporated in a aqueous dispersion, emulsion, or solution containing the admixture or admixtures. For example, a corrosion inhibitor admixture, such as a calcium nitrite dispersion, can be mixed with Portland cement and allowed to harden into a mass and then crushed to form the particulates.
Alternatively, or in addition to the admixture-intermixing method, the particulates can be coated with one or more admixtures. The particulates provide a high loading surface. In further embodiments of the invention, the particulates may contain one or more intermixed admixtures (e.g., calcium nitrite) and be coated with one or more other admixtures (e..g., polyoxyalkylene water reducers (or so-called superplasticizers), polyoxyalkylene shrinkage reduction admixtures, or other admixtures). This provides a means for simultaneous use of admixtures or agents that are not easily compatible (if otherwise used in the same solution).
When viewed under microscope, the surfaces of comminuted substantially hydrated cementitious particulates of the present invention are highly granular, and even microscopically granulose in nature. The particulates are not only xe2x80x9cgranularxe2x80x9d but are microscopically xe2x80x9cgranulosexe2x80x9d because they have small granulate surface textures or granules upon the individual granule particulates.
Thus, the particulates of the invention provide an excellent and novel carrier particle system for delivering chemical additives, such as admixtures, into castable matrix compositions (such as concrete, mortar, masonry), sprayable matrix compositions (such as shotcrete or sprayable fireproofing, such as gypsum-based fireproofing), coating compositions (such as latex and non-aqueous paints, primers), as well as adhesive compositions. When an admixture such as calcium nitrite is incorporated into a concrete using the inventive particulates, it was suprisingly found that the calcium nitrite retains its ability to provide corrosion inhibition even though it is introduced into the concrete while initially embedded in hydrated cement. As another example, the particulates of the invention may be used to incorporate an admixture such as calcium nitrite into a paint or coating composition, such as epoxy coating for steel rebar.
The inventors believe that significant advantages may be obtained by the process of the invention, not only in terms of avoiding time-consuming labor, energy costs, and processing complexity; but also convenience in loading a high level of admixture(s) per unit of carrier material and in obtaining uniform dosing practice. In intermixing and hydrating together the admixture(s) and hydratable cementitious binder, high admixture-to-cement ratios of at least 10%, and more preferably at least 12% to 90%, and more preferably 15-60%, by weight of admixture(s) on weight of cement, are believed to be realizable through the process of the invention.
The use of cement in making cementitious-admixtures particulates also permit lower water/cement ratios in the final concrete, mortar, masonry, fireproofing, or shotcrete composition in comparison to using conventional liquid admixtures. Moreover, the inventors believe that hydrated cement avoids incompatibility problems that sometimes arises between admixtures and cement, and would not be detrimental to the final composition.
The present invention also provides methods for modifying matrix compositions, such as castable cementitious compositions (e.g., ready-mix concrete, pre-cast concrete, mortar, grout, masonry concrete, shotcrete, gypsum, plaster), as well as latex and non-aqueous polymers (e.g., acrylic, alkyd, epoxy, polyester, urethane), by introducing the above-described particulates into the matrix or coating composition to be modified.
Further advantages and features of the invention are described hereinafter.